RU2789583C2 - Integrated methods for production of p-xylol - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to three options of a method for the production of p-xylol. According to one of options, the method includes stages, at which: in a xylol column, a flow of aromatic hydrocarbons C₈ and a flow of hydrocarbons C₉ ⁺ are separated from at least part of an ethylbenzene-containing supplied flow; in a xylol separation zone, a p-xylol-enriched product is separated from at least part of the flow of aromatic hydrocarbons C₈ to obtain a p-xylol-depleted waste flow; in an isomerization zone, isomerization of at least part of the p-xylol-depleted waste flow is carried out to obtain xylol-equilibrium isomerizate. At least part of xylol-equilibrium isomerizate is recycled into the xylol column. In an ethylbenzene (hereinafter – EB) separation module, an ethylbenzene-enriched product is separated from (i) part of the ethylbenzene-containing supplied flow to obtain an ethylbenzene-depleted supplied flow, and at least part of the ethylbenzene-depleted supplied flow is connected to all or part of the flow of aromatic hydrocarbons C₈; (ii) part of the flow of aromatic hydrocarbons C₈ to obtain an ethylbenzene-depleted flow of aromatic hydrocarbons C₈, and at least part of the ethylbenzene-depleted flow of aromatic hydrocarbons C₈ is connected to part of the flow of aromatic hydrocarbons C₈, conducted via a bypass outside EB separation module; (iii) part of the p-xylol-depleted waste flow to obtain an ethylbenzene and p-xylol-depleted waste flow, and at least part of the ethylbenzene and p-xylol-depleted waste flow is connected to part of the p-xylol-depleted waste flow, conducted via a bypass outside EB separation module; (iv) part of xylol-equilibrium isomerizate to obtain ethylbenzene-depleted xylol-equilibrium isomerizate, and at least part of ethylbenzene-depleted xylol-equilibrium isomerizate is connected to part of xylol-equilibrium isomerizate, conducted via a bypass outside EB separation module, or (v) combination thereof. In this case, EB separation module contains extractive distillation, wherein extractants with a carbocyclic (for example, aromatic) or heterocyclic ring structure are used, substituted in ring positions, where substitution is possible (i) with at least one NR^aR^b radical (i.e., substitute -NR^aR^b), wherein R^a and R^b are independently selected from a group consisting of an oxygen radical, a hydrogen radical, and a hydrocarbyl radical including from about 1 to about 20 carbon atoms, and (ii) at least two halogen radicals (i.e., halogen substitutes formed of their respective halogen atoms).

EFFECT: present invention allows for efficient extraction of ethylbenzene and other components boiling at a temperature close to the boiling point of xylene isomers.

18 cl, 5 dwg, 1 ex

Description

CROSS-REFERENCE TO RELATED APPLICATION

[01] This application claims priority to U.S. Provisional Application No. 62/701085, filed July 20, 2018, the contents of which are expressly incorporated herein by reference in their entirety.

FIELD OF TECHNOLOGY

[02] The present invention relates to processes for the production of para-xylene from a crude ethylbenzene-containing feed stream comprising mixed isomers of xylene, such as a naphtha reformate or naphtha pyrolysis gasoline. Para-xylene production is integrated with an ethylbenzene separation process (eg by extractive distillation) to recover ethylbenzene.

BACKGROUND OF THE INVENTION

[03] Xylene (dimethylbenzene) isomers, namely ortho-xylene, meta-xylene and para-xylene, are important chemical intermediates, while para-xylene is of much greater industrial importance. The most important process in which para-xylene is used is its oxidation to terephthalic acid. Terephthalic acid, in turn, is used to make polymers such as polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). PET, one of the world's largest production polymers, is produced by the condensation polymerization of terephthalic acid with ethylene glycol. Given the large market for PET plastics and fibers, as well as other end products made from para-xylene, there is a high demand for this high purity intermediate.

[04] As a source of xylene isomers, the petroleum refining process known as reforming generally results in the conversion (or "aromatization") of the original hydrocarbon naphtha, which is a fraction of crude oil, into such C ₈ aromatics, in addition to benzene and toluene, which Also important products. The effluent from the reaction zone of the reformer, or reformer (for example, a catalytic reformer with continuous catalyst regeneration or semi-regenerative type regeneration), is separated by distillation, in particular by means of a reformate splitter. C ₆ and C ₇ aromatics, namely benzene and toluene, are often removed in the splitter overhead, while C ₈ aromatics, namely xylene isomers as well as ethylbenzene, are essentially completely recovered in the splitter bottoms, approximately , in equilibrium concentrations. The higher boiling C ₉ and C ₁₀ aromatics present in the reformate splitter bottoms are typically separated by subsequent distillation, for example using a xylene splitter or xylene column, from the C ₈ aromatics and ethylbenzene of this stream. A similar separation, involving the removal of low boiling C ₆ /C ₇ aromatics and/or high boiling C ₉ /C ₁₀ aromatics, can be performed for other known industrial products such as naphtha pyrolysis gasoline to increase the concentration of mixed xylenes and Ethylbenzola in fractions obtained from these products.

[05] High value para-xylene can be separated from a stream of mixed xylenes and ethylbenzene, for example, obtained as a low-boiling fraction (eg, overhead) of a xylene column, as described above, using a para-xylene separation method. Due to the close boiling points of xylene isomers, methods for separating xylenes by distillation are not cost-effective. In contrast, adsorption separation is usually used for this purpose using a simulated moving bed (SMB) of an adsorbent having micropores of such a size and geometry that provide selective adsorption of para-xylene relative to other xylene isomers. Typical adsorbents and methods for selectively separating para-xylene in this way are described in, for example, US 5,495,061 and US 5,948,950. in accordance with the method described in US 5329061.

[06] Regardless of the particular process used to separate and recover to use para-xylene, a para-xylene depleted effluent stream is obtained at the end. In the case of SMB, separation using an adsorbent, this effluent may be referred to as "raffinate", while in the case of crystallization it is usually referred to as "slop filtrate". Downstream of the xylene separation zone, the para-xylene depleted effluent stream, containing predominantly ortho-xylene and meta-xylene, is typically further processed in an isomerization reaction zone to restore an approximately equilibrium concentration of xylene isomers, including about 20-25 wt. para-xylene. The para-xylene formed from the isomerization can advantageously be recycled to the xylene separation zone for separation and recovery, thereby increasing the overall yield of para-xylene recovery, while the other xylene isomers are recycled substantially to extinction. Alternatively, the isomerization zone product or "isomerizate" may be recycled to the xylene column so that C ₉ , C ₁₀ and/or heavier hydrocarbons (particularly aromatic hydrocarbons) can be continuously removed reaction products. In any case, industrial processes implement successive para-xylene separation zones (by selective adsorption or selective crystallization) and isomerization in combination with recirculation of less desirable xylene isomers in order to recover para-xylene from C ₈ aromatic hydrocarbon products, including those obtained in catalytic reforming, naphtha cracking and other processes.

[07] It is generally desirable to have a substantially closed loop formed by continuous recirculation of the isomerate to either the para-xylene separation zone and/or the upstream xylene column to maximize overall product recovery. However, this is known to lead to the accumulation of certain components continuously flowing into this process loop, since their boiling point is close to that of the xylene isomers and makes them difficult to remove during normal upstream distillation. (eg, in the reformate separator or xylene column described above). One such component is ethylbenzene, which, depending on the catalyst used in the isomerization reaction zone, isomerizes only to a certain extent in the isomerization zone to form mixed xylenes, from which, ultimately, additional para-xylene can be obtained and recovered. . Methods for separating ethylbenzene by intensive distillation (for example, using multiple columns) have proven to be uneconomical.

[08] The goal of alternative technical solutions aimed at limiting the excessive accumulation of ethylbenzene is the conversion of this component, for example, by increasing the degree to which it isomerizes to xylenes and / or dealkylates (or cracks) to benzene and ethylene, which are easier to separate into this technological circuit. The formation of benzene does not pose a serious problem, since it is still an aromatic hydrocarbon that can be converted to xylenes by disproportionation and/or transalkylation reactions, which are often included in complex aromatic processing processes. However, enhancing the functionality of the catalyst for the conversion of ethylbenzene in the isomerization zone (either by dealkylation or due to intensification of isomerization) inevitably led to a corresponding activation of non-selective side reactions and the formation of other by-products that are less valuable and/or more difficult to convert into the desired components.

[09] Specific examples of such by-products are non-aromatic (eg, paraffinic, cycloparaffinic and/or naphthenic) hydrocarbons, which, like the ethylbenzene to be removed, can also accumulate in the process loop. Non-aromatic hydrocarbons and other by-products also contribute to the overall lost product yield and therefore adversely affect the economics of the process. The same adverse effects occur when conditions in the isomerization zone, as opposed to just changing the catalyst composition (eg, increasing the acidity of the catalyst support to promote cracking), are adjusted to promote conversion of ethylbenzene. That is, the more severe operating conditions required to carry out the reaction of this component lead to the formation of non-aromatic hydrocarbons and other by-products, which also generally reduces the yield of para-xylene. Recently, the use of an additional dehydrogenation reactor downstream of the isomerization reactor has been proposed to compensate, at least in part, for the formation of by-products by converting naphthenic hydrocarbons to more desirable aromatic hydrocarbons.

[10] However, any catalyst composition and/or process conditions aimed at promoting reactions other than xylene isomerization, such as isomerization or dealkylation of ethylbenzene or, otherwise, dehydrogenation of naphthenic hydrocarbons, as described above, is inevitably associated with increased costs and increasing complexity in the production of para-xylene in accordance with conventional technology. The use of more stringent isomerization operating conditions for the conversion of ethylbenzene can entail the introduction and recycling of hydrogen, which is associated with significant capital and operating costs. In addition, the proposals received so far have not finally resolved the issue of the loss of the aromatic ring, i.e., the formation of non-aromatic hydrocarbons in side reactions, as a consequence of the conversion of ethylbenzene.

[11] In general, the production of para-xylene is commercialized in large-scale plants, and, in terms of costs, various manufacturers in this industry are in a highly competitive environment. Therefore, the refinery and petrochemical industry must constantly strive to achieve the best possible technical and economic parameters (for example, conversion, separation and recovery for use) of integrated process units in the most cost-effective way (for example, in terms of capital or operating costs). To this end, Meyers et al ., Handbook of Petroleum Refining Processes, ^4th Edition (2016) describes a conventional complex aromatics processing unit. There is still a need in the industry for a process for the production of para-xylene from products containing C ₈ aromatics that provides an effective solution to the issue of accumulation of ethylbenzene and other components in the process loop.

SUMMARY OF THE INVENTION

[12] The present invention relates to the discovery of processes for the production of para-xylene, integrated with efficient removal and recovery in order to use ethylbenzene and other components boiling at a temperature close to the boiling point of the xylene isomers. These components generally refer to hydrocarbons other than xylenes, which are formed in the process and/or introduced into the process and which have such a boiling point that the costs associated with conventional distillation do not justify the results obtained when separating and recovering such components from xylenes-containing process streams, including those forming the technological circuit of the para-xylene production process. Such components may generally have a boiling point close to within 15°C (+/-15°C or +/-27°F), within 10°C (+/-10°C or +/- 18°F) or to within 5°C (+/-5°C or +/-9°F) the boiling point of para-xylene (138°C or 280°F) and therefore includes paraffinic hydrocarbons in addition to ethylbenzene C ₈ (eg n-octane and isomers of iso-octane), C ₇ -C ₈ cycloparaffin hydrocarbons (eg ethylcyclohexane and cyclooctane), C ₉ naphthenic hydrocarbons (eg trimethylcyclohexane isomers) and other non-aromatic compounds.

[13] In the absence of separation and recovery, such as by extractive distillation as described herein, these components must be converted to products (e.g., benzene and ethylene in the case of ethylbenzene cracking) from which, ultimately, can be obtained para-xylene (for example, by transalkylation) or, otherwise, products that can be removed at some point in the para-xylene production process. For example, C ₁₂ hydrocarbons formed as a by-product of various reactions such as ethylbenzene cracking can be removed in the C ₉ ⁺ hydrocarbon stream as a high boiling fraction from xylene column separation. As described above, conventional processes for the production of para-xylene use their conversion to avoid excessive accumulation of low-boiling components in the process cycle for the production of para-xylene. Modification of isomerization catalysts and/or isomerization operating conditions to effect such conversion (eg, ethylbenzene isomerization, ethylbenzene cracking, and/or naphthenic hydrocarbon dehydrogenation) causes non-selective side reactions that ultimately reduce para-xylene production efficiency.

[14] The present invention, in contrast, is concerned with the discovery of processes for the production of para-xylene, in which ethylbenzene and other components near boiling with xylene isomers can be recovered as products without significant conversion. Advantageously, the isomerization zone (eg, the conditions in the isomerization reactor and/or the isomerization catalyst used in the reactor) may be substantially or entirely dedicated to the isomerization of ortho-xylene and meta-xylene to para-xylene. In accordance with some embodiments of the invention, this may require less stringent and/or less complex operating conditions, such as a liquid-phase (rather than vapor-phase) process in an isomerization zone (or an isomerization reactor in this zone), without the need for introducing hydrogen and its corresponding recycle, waste (eg, in the ethylbenzene cracking reaction) and inevitable losses (eg, losses to the gaseous purge stream and/or liquid stream solution).

[15] In addition to reducing hydrogen consumption compared to conventional para-xylene production processes, the recovery of ethylbenzene in accordance with the methods described herein can provide additional economic benefits in terms of reduced yield of by-products, in particular those formed during conventional isomerization, where the efficiency of the conversion of ethylbenzene is a characteristic property of the isomerization catalyst and/or the process conditions used. Such by-products are non-aromatic hydrocarbons associated with aromatic ring loss reactions, as well as light hydrocarbon gases (eg ethylene) associated with cracking reactions. Therefore, the processes described herein may include an ethylbenzene (EB) separation module (for example, using extractive distillation) to recover ethylbenzene and thereby increase the yield of liquid products, including, for example, an ethylbenzene-enriched product that has an economic value for the subsequent production of styrene monomer. In addition, by relaxing or eliminating the need for the conversion of ethylbenzene in the isomerization zone, including eliminating the introduction of hydrogen for cracking ethylbenzene, the yield of low-value gaseous products (for example, hydrogen-containing purge streams that include a by-product - ethylene) can be significantly reduced. The cost of the means of supply (eg hydrogen recycle compressor) can also be reduced.

[16] It will be appreciated by those skilled in the art that even a small improvement in any of the above parameters, such as a reduction in hydrogen consumption, by-product yield and/or support requirements, and an increase in para-xylene yield and/or overall value product (for example, through the formation of an ethylenebenzene-enriched product) can provide significant economic benefits.

[17] These and other embodiments and aspects related to the present invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[18] FIG. 1-4 show exemplary processes for recovering para-xylene from, for example, a crude ethylbenzene containing feed stream, in which an ethylbenzene (EB) separation module is applied at various alternate points in the process to prevent excessive accumulation of ethylbenzene in the process streams.

[19] FIG. 5 shows a typical extractive distillation process, for example, which may be a specific type of EB separation module integrated into the process shown in FIG. 1-4.

[20] The elements shown in FIG. 1-5 are not necessarily drawn to scale and should be considered as reflecting a schematic explanation of exemplary embodiments of the invention and/or its principles. For ease of understanding, equipment such as reactors and other vessels, valves, pumps, compressors, heat exchangers, meters and auxiliary process streams, the presence of which is obvious to those skilled in the art based on the present description, are not shown. Methods corresponding to other embodiments of the invention will have configurations, components, and operating parameters determined, in part, by the applications for which they are intended and the environment in which they will be used.

DETAILED DESCRIPTION

General terms

[21] In the embodiments described herein, the separation of ethylbenzene is used to improve the overall profitability of para-xylene production. For this separation, in certain embodiments of the invention, a standard process for separating and / or recovering ethylbenzene and / or other products is used to increase the overall value of the product stream obtained from the para-xylene production process, while this standard process is called "EB separation module" and can be used at various points in the para-xylene production process. The separation of ethylbenzene, for example, using an EB separation module can be carried out, for example, by extraction, distillation, or a combination of extraction and distillation, which combination is the preferred separation method, referred to as extractive distillation and is described in more detail below. Distillation, used alone or in combination with extraction, may be distillation at elevated or reduced pressure, and may include the introduction of an upward flow of gas (stripping agent) or a downward flow of liquid (solvent) to facilitate said separation. In accordance with preferred embodiments of the invention, the EB separation module described herein may include extractive distillation, and the preferred EB separation module is an extractive distillation zone.

[22] In the context of this document, steps such as "separation", "isomerization", "recycling", "removal" (for example, by extractive distillation) can be described as being carried out in relation to "at least part" of a certain technological a stream (eg, a crude ethylbenzene-containing feed stream, a C ₈ aromatic hydrocarbon stream, a para-xylene-depleted effluent stream, or a xylene-equilibrium isomerate). Therefore, the step may be performed on the entire stream, essentially the entire stream (eg, at least about 95%), or some other portions (eg, at least about 50%) of the stream. Therefore, the phrase "at least a portion" is intended to emphasize the possibility of intermediate separations (eg, distillation) to remove some fraction (eg, enriched in an impurity such as C ₇ ^- hydrocarbons) of the specified process stream. In addition, this expression takes into account the possibility that some of this process stream, where appropriate, can be removed to reduce the load on the equipment, prevent the accumulation of by-product, sampling, etc.

[23] Although processes for the production of para-xylene use the above steps and/or other steps described herein, for example, when forming a process loop for the production of para-xylene, this does not exclude the possibility of having one or more additional stages or operations along the stream. before and/or after the described stage, such as mixing (for example, with an auxiliary feed stream for this stage), separation (for example, an intermediate product stream), bypassing the described stage (for example, part of the process stream), recycling to any stage ( eg parts of a process stream) and/or reaction (eg to convert undesired components and/or increase the yield of desired components). In the case of separation, typical additional steps or operations include removal of dealkylated products ⁽ eg, benzene) downstream of the para-xylene separation zone or removal of the hydrocarbon-rich C ₇ fraction downstream of the isomerization zone. In the case of recycling, a typical additional step or operation is the recycling of a portion of the xylene equilibrium isomerate downstream of the isomerization zone to the xylenes separation zone. In the case of a reaction, a typical additional step or operation is transalkylation or disproportionation, the reaction between C ₇ aromatics (eg toluene) and C ₉ aromatics (eg trimethylbenzene) to form xylenes downstream of the isomerization zone.

[24] However, in some instances, the process may be carried out without any one or any combination of such mixing, separating, bypassing, recirculating and reacting steps downstream before and/or after any of the described steps or any two or more several stages described. In accordance with specific embodiments of the invention, the methods may be implemented with the additional step of separating the enriched C ₇ hydrocarbon fraction from the xylene equilibrium isomerate and/or reacting at least a portion of the xylene ^equilibrium isomerate in a transalkylation zone. In these embodiments, at least a portion of the C ₇ ^- depleted xylene equilibrium isomerate produced and/or at least a portion of the resulting transalkylation zone effluent (with an increased concentration of xylenes relative to the xylene equilibrium isomerate) may be recycled. into the xylene column, while the resulting streams still contain at least part of the xylene-equilibrium isomerizate.

[25] The steps described herein produce fractions referred to as "overheads" and "bottoms", which can be withdrawn from the top or bottom of the respective distillation column. However, "overhead" may also be referred to as "low boiling point", which more broadly encompasses any fraction having greater volatility (lower boiling point range) and/or lower distillation end point than feedstock and/or with the "bottom strap" of the corresponding distillation column. Similarly, the "bottom cut" may also be referred to as the "high-boiling cut", which broadly encompasses any cut that has less volatility (higher boiling range) and/or a higher initial boiling point than the feedstock and/ or the overhead of the respective distillation column, wherein the overhead is the overhead as defined above. Temperatures of the beginning and end of the boil can be determined in accordance with ASTM D86.

[26] The process parameters for ethylbenzene conversion and aromatic ring loss are defined herein based on a single pass through the isomerization zone (e.g., the isomerization reactor in this zone) and based on total conversion (i.e., the conversion of ethylbenzene fed into the production process loop). para-xylene and the loss of aromatic rings introduced into the process circuit for the production of para-xylene). The yield of para-xylene can also be determined on a "single" or "total" basis. Single output (or recovery) means the amount of para-xylene fed to the xylenes separation zone (for example, para-xylene in or part of the C ₈ aromatics stream or, otherwise, total para-xylene in the ethylbenzene-depleted aromatics stream C ₈ and the portion of the C ₈ aromatic hydrocarbon stream bypassed outside of the extractive distillation), which is present in the para-xylene-enriched product effluent from the xylenes separation zone. Total Yield refers to that total amount of xylenes fed into the process, such as the amount fed to the para-xylene production process loop described herein (eg, the total amount of xylenes in the crude ethylbenzene-containing feed stream), that is present in the form of para-xylene in a para-xylene enriched product. Therefore, the single yield is based on a 100% yield corresponding to the total recovery of para-xylene fed to the xylene separation zone in the para-xylene enriched product, while the overall yield is based on a 100% yield corresponding to the total ortho-xylene conversion. and meta-xylene fed into the process to para-xylene (i.e., recycling until these isomers disappear in the para-xylene production loop) and hence the total recovery of all xylenes introduced into the process in the form of para-xylene.

[27] In a para-xylene separation zone, including either adsorption separation or crystallization, the single yield and/or the total para-xylene yield may be greater than about 60%, greater than about 90%, greater than about 95%. or more, about 98%. The degree of purity of the para-xylene-enriched product is generally such that the product contains more than about 93% by weight, more than about 97% by weight, more than about 99% by weight. or even more, about 99.7 wt%. para-xylene. Those skilled in the art will recognize that there is generally a trade-off between para-xylene recovery, or single yield, and the purity of para-xylene according to the purity/recovery curve associated with the process.

[28] The crude ethylbenzene-containing feed stream used in the processes described herein includes any mixture of ethylbenzene and xylenes from which para-xylene can be economically recovered using a combination of para-xylene separation and isomerization of the resulting para-xylene-depleted effluent. stream (eg raffinate or off-spec filtrate). A typical raw ethylbenzene-containing feed stream contains C ₈ aromatics in a total amount of more than about 50% by weight, more than about 75% by weight. or more, about 95 wt%. At least a portion of the remaining components of this feed stream may be C ₉ ⁺ hydrocarbons, including C ₉ aromatics. For example, the crude ethylbenzene-containing feed stream may contain C ₉ ⁺ hydrocarbons in an amount of less than about 20% wt., less than about 10% wt. or less, about 5 wt%. In general, all or substantially all (eg, greater than about 95 wt %) of these C ₉ ⁺ hydrocarbons may be suitably removed in a xylene column as described herein and/or in an EB separation module. When such a removal is carried out, the resulting C ₈ aromatics stream may be, for example, an overhead or low-boiling fraction of a xylene column and may contain C ₈ aromatics in a total amount of more than about 85 wt%, more than about 95 wt%. or more, about 98 wt%.

[29] For both the crude ethylbenzene-containing feed stream and the C ₈ aromatics stream (e.g., the C ₈ aromatics fraction of this stream), ethylbenzene may be present in an amount typically from about 3 wt. up to about 75 wt%. depending on the source of the crude ethylbenzene-containing feed stream. For example, the crude ethylbenzene-containing feed stream may include a naphtha reformate, a naphtha cracker (eg, pyrolysis gasoline), a transalkylation product (eg, an effluent from the reaction of toluene and C ₉ aromatics to form C ₈ aromatics), or any combination of several of these products. . In the case of a crude ethylbenzene-containing feed stream containing, consisting of, or consisting essentially of (for example, comprising more than 95 wt. %) naphtha reformate, ethylbenzene may be present in the feed stream in an amount of from about 5 wt. up to about 45 wt%. or from about 10% wt. up to about 35% wt. In the case of a crude ethylbenzene-containing feed stream containing, consisting of, or consisting essentially of (e.g., comprising more than 95 wt. %) naphtha cracking product (e.g., pyrolysis gasoline), ethylbenzene may be present in the feed stream in an amount of from, about , 25% wt. up to about 75 wt%. or from about 35 wt%. up to about 65 wt%. In the case of an unpurified ethylbenzene-containing feed stream containing, consisting of, or consisting essentially of (for example, comprising more than 95 wt. %) the transalkylation product, ethylbenzene may be present in the feed stream in an amount of from about 1 wt. up to about 25% wt. or from about 2% wt. up to about 15% wt. Typical products of naphtha reforming, naphtha cracking and/or transalkylation are those products from which benzene and toluene have been separated upstream as overhead, for example using a reformate separator as described herein.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[30] Embodiments of the invention are directed to a process for producing para-xylene, the process comprising: separating a C ₈ aromatic hydrocarbon stream and a C ₉ ⁺ hydrocarbon stream from a crude ethylbenzene-containing feed stream in a xylene column. The C ₈ aromatics stream may be a low boiling fraction enriched in C ₈ aromatics and depleted in C ₉ ⁺ hydrocarbons compared to the crude ethylbenzene containing feed stream, while the C ₉ ⁺ hydrocarbon stream may be a high boiling fraction enriched in C ₉ ⁺ hydrocarbons and depleted in C ₈ aromatics compared to the raw ethylbenzene-containing feed stream. Typical raw ethylbenzene-containing feed streams include a mixture of ethylbenzene and xylenes, for example a mixture derived from naphtha reforming, naphtha cracking (e.g. pyrolysis gasoline) and/or transalkylation (e.g. conversion products of toluene and C ₉ aromatics to C ₈ aromatics ). For example, such mixtures can be obtained after removing C ₇ ^- hydrocarbons from such products in a low-boiling fraction, which is separated in an upstream separator.

[31] The method may also include: separating, in a xylene separation zone, a para-xylene-enriched product from at least a portion of the C ₈ aromatics stream to form a para-xylene depleted effluent stream. Where pseudo-moving bed (SMB) adsorption is used in the xylene separation zone, the para-xylene depleted effluent may be a raffinate produced in the manner described above. Where crystallization is used in the xylene separation zone, the para-xylene depleted effluent may be a slop filtrate as described above.

[32] The process may also include isomerizing at least a portion of the para-xylene-depleted effluent stream in an isomerization zone to form a xylene-equilibrium isomerate. This product can have xylene isomer concentrations (ortho-xylene, meta-xylene and para-xylene) closer to equilibrium concentrations compared to the para-xylene depleted effluent stream. The process may further comprise recycling at least a portion, preferably all, of the xylene equilibrium isomerate to the xylene column. Recycling may result in a para-xylene production loop, as described in more detail herein.

[33] The isomerization zone or isomerization reactor in this zone can be operated as described herein with relatively low ethylbenzene conversion and/or loss of aromatic ring, and any of these parameters can be measured on a "single" basis (in one pass ) from the inlet to the isomerization zone (or isomerization reactor) (eg, para-xylene depleted effluent) to the exit of the isomerization zone (or isomerization reactor) (eg, xylene-equilibrium isomerizate).

[34] For example, a single conversion of ethylbenzene can be calculated as a percentage according to

[1-(EB _RXOUT /EB _RXIN )] x 100,

[35] where EB _RXOUT is the weight of ethylbenzene exiting the isomerization reactor (e.g. present in the xylene equilibrium isomerate) and EB _RXIN is the weight of ethylbenzene entering the isomerization reactor (e.g. present in the para-xylene depleted effluent or part thereof, supplied to this reactor). The weight values of ethylbenzene at the inlet or outlet of the isomerization reactor can be calculated (eg, at steady state) based on the weight percentage of ethylbenzene in the respective inlet and outlet process streams, multiplied by the respective weight or mass flow rate of these streams. In typical embodiments of the invention, the isomerization zone (or the isomerization reactor in this zone) is operated such that a single conversion of ethylbenzene is less than about 5%, less than about 2%, or less than about 1%.

[36] One-time aromatic ring loss can be calculated as a percentage according to

NONAROM _RXDELTA /AROM _RXIN x 100,

[37] where NONAROM _RXDELTA means the number of moles of non-aromatic hydrocarbons formed in the isomerization reactor (for example, the number of moles present in the xylene-equilibrium isomerate minus the number of moles present in the para-xylene depleted effluent stream or part of it fed to this reactor) , and AROM _RXIN means the number of moles of aromatic hydrocarbons at the inlet to the isomerization reactor (for example, the number of moles present in the para-xylene depleted effluent stream or part of it fed to this reactor). The number of moles of non-aromatic hydrocarbons formed in the isomerization reactor, as well as the number of moles of aromatic hydrocarbons at the inlet to this reactor can be calculated (for example, in steady state operation) based on the weight percentage of non-aromatic and aromatic hydrocarbons divided by the corresponding molecular weight, in the corresponding incoming and outgoing process streams and multiplied by the weight or mass flow rate of the corresponding stream. In exemplary embodiments of the invention, the isomerization zone (or the isomerization reactor in this zone) is operated such that one-time aromatic ring loss is less than about 5%, less than about 2%, or less than about 1%.

[38] Alternatively, ethylbenzene conversion and aromatic ring loss can be measured on a "total" basis for total process feed (e.g., crude ethylbenzene-containing feed stream) relative to total process output (e.g., para-xylene enriched ethylbenzene-rich product, non-aromatic rich product stream and C ₉ ⁺ hydrocarbon stream). The total input and output amounts may correspond to the amounts described herein supplied to and output from the para-xylene production process loop, or, alternatively, may include additional input and output amounts in streams additionally added to or removed from this loop (for example, the amount in the C ₇ ^-rich effluent withdrawn as the overhead of the heptane removal column). Thus, the total conversion of ethylbenzene and the total loss of the aromatic ring can be determined, respectively, as

1-(EB _PROCESSOUT /EB _PROCESSIN ) x 100 and NONAROM _PROCESSDELTA /AROM _PROCESSIN x 100,

[39] as described above for these parameters determined on a one-time basis. Therefore, EB _PROCESSOUT and EB _PROCESSIN mean the weight of ethylbenzene at the output and input of the process, respectively (for example, at the output and input of the para-xylene production loop, as described in this document), and NONAROM _PROCESSDELTA and AROM _PROCESSIN mean, respectively, the number moles of non-aromatic hydrocarbons formed in the process, and the number of moles of aromatic hydrocarbons at the inlet to the process. In typical embodiments, the process is carried out such that the overall conversion of ethylbenzene is less than about 50%, less than about 20%, less than about 10%, or even less than about 2%. These ranges may reflect the percentage conversion of ethylbenzene introduced into the para-xylene production process loop (eg, under steady state conditions). In other exemplary embodiments of the invention, the process is carried out such that the total aromatic ring loss is less than about 10%, less than about 5%, or even less than about 2%. These ranges may reflect the percentage loss of aromatic rings introduced into the para-xylene production loop (eg, under steady state conditions).

[40] Determined both on a single and overall basis, relative low compared to conventional methods, ethylbenzene conversion and loss of aromatic ring may be associated with reduced requirements for the conversion of ethylbenzene in the isomerization zone (for example, by isomerization or cracking, as described above) and hence milder operating conditions and/or simplified isomerization catalyst compositions. These effects, in combination, can increase the yield of para-xylene; reducing the need for means of supply, hydrogen consumption and the output of by-products; and the formation of a highly valuable product enriched in ethylbenzene.

[41] In accordance with exemplary embodiments of the invention, extractive distillation or another separation method (e.g., in an EB separation module) is used to remove ethylbenzene from at least a portion of one or more of the streams identified above (e.g., crude ethylbenzene-containing feed stream, C ₈ aromatics stream, para-xylene-depleted effluent stream, and/or xylene-equilibrium isomerizate). In accordance with other exemplary embodiments of the invention, after separating the ethylbenzene (e.g., producing an ethylbenzene-rich product), at least a portion of the resulting ethylbenzene-depleted stream (e.g., an ethylbenzene-depleted C ₈ aromatics stream, an ethylbenzene-depleted and para-xylene-depleted effluent stream and/or ethylbenzene-depleted xylene-equilibrium isomerizate) is combined with a bypass portion of the stream outside of the extractive distillation. That is, at least a portion of one or more of the streams above is used as feedstock to an EB separation module (e.g., extractive distillation zone) and the resulting ethylbenzene-depleted stream is recycled to the process (e.g., recycled to the para-xylene production loop). ) in the same stream (for example, without performing any intermediate separation or conversion of the stream conducted through the bypass outside the EB separation module before connection with the resulting ethylbenzene depleted stream).

[42] Thus, the portion of a given process stream that is bypassed outside the EB separation module may refer to the stream that is separated from the portion used as raw material of that module, and which bypassed portion forms all or part of the production process loop stream para-xylene, such as all or part of (i) a C ₈ aromatics stream, (ii) a para-xylene depleted effluent stream, or (iii) a xylene equilibrium isomerate, as described herein. Preferably, the bypassed portion forms a para-xylene production process loop stream corresponding to the portion used as feedstock of the EB separation module, for example in the case of (i) a portion of the C ₈ aromatics stream supplied to the EB separation module and the bypassed portion forms a stream of aromatic hydrocarbons WITH ₈ process circuit for the production of para-xylene; (ii) a portion of the para-xylene depleted effluent stream fed to the separation module EB and the bypassed portion forms a para-xylene depleted effluent from the para-xylene production process loop, or (iii) a portion of the xylene-equilibrium isomerate fed to the separation module EB and the bypassed part forms the xylene-equilibrium isomerizate of the para-xylene process circuit. In the case of separating the ethylbenzene-rich product from all or part of the crude ethylbenzene-containing feed stream, it is also possible to combine the resulting ethylbenzene-depleted feed stream with all or part of the C ₈ aromatics stream. In this case, the portion of the crude ethylbenzene-containing feed stream bypassed outside the separation module EB (bypass portion) may form all or part of the xylene column fresh feed stream, so that the fraction of this fresh feed stream, namely that contained in the C aromatics stream ₈ removed as xylene column overhead may be fed into the para-xylene production process loop. In this respect, specific aspects of the invention relate to increased process flexibility in the implementation of para-xylene production processes. Advantageously, smaller or larger amounts of feed portions of a given process stream may be fed to the EB separation module, regardless of where it is located in the para-xylene production process loop, and accordingly, larger or smaller quantities of bypass portions of this stream may be used to form contour. This provides significant advantages in terms of controlling the process according to changes in the quality of the raw ethylbenzene containing feed stream (e.g. its ethylbenzene content) considering the economics of trade-off between higher throughput of the EB separation module with the potential to achieve higher recovery of ethylbenzene and higher throughput. a para-xylene production process loop with the potential to reduce the process load (e.g. support requirements) on the EB separation module.

[43] Advantageously, exemplary methods may further comprise removing without conversion all or substantially all (e.g., greater than about 80%, greater than about 90%, or greater than about 95%) ethylbenzene introduced into a process such as the para-xylene production loop described herein. The degree of conversion of ethylbenzene, which can be measured on a single or total basis, as described herein, will depend on the operating conditions and the catalyst in the isomerization reaction zone (for example, on the catalyst and reaction conditions in the isomerization reactor), which, as described above, can lead to a reduction in side reactions compared to conventional methods that do not use extractive distillation to separate ethylbenzene. With respect to a given process loop, all or substantially all (e.g., greater than about 80%, greater than about 90%, or greater than about 95%) of the ethylbenzene introduced may be present in the crude containing ethylbenzene feed stream fed to the xylene column. The extent to which ethylbenzene is introduced into the process loop will depend on the operation of the xylene column and its efficiency in separating ethylbenzene into the C ₈ aromatics stream.

Method and technological circuit for the production of para-xylene

[44] In accordance with the typical method shown in FIG. 1, the crude ethylbenzene-containing feed stream 2 described above is fed to a xylene column 100 to separate C ₈ aromatics stream 4 as the low-boiling fraction ⁽ or overhead) and stream 12 C ₉₊ hydrocarbons as the high-boiling fraction (or bottoms stream). Portion 4A of C ₈ aromatics stream 4 is fed to EB separation module 400 (e.g., extractive distillation zone) to separate ethylbenzene-rich product 402 and optionally also non-aromatics-rich stream 401 to produce ethylbenzene-depleted C ₈ aromatics stream 4B. The non-aromatic rich stream 401, if produced, is enriched (or has a higher concentration) in non-aromatic compounds than the C ₈ aromatics stream 4 . Non-aromatic hydrocarbons present in the non-aromatic rich stream 401 may include C ₈ paraffinic hydrocarbons (e.g., n-octane and iso-octane isomers), C ₇ -C ₈ cycloparaffinic hydrocarbons (e.g., ethylcyclohexane and cyclooctane), and/or C naphthenic hydrocarbons. ₉ (for example, isomers of trimethylcyclohexane), the boiling point of which is close to the boiling point of C ₈ aromatic hydrocarbons. Enriched with non-aromatic compounds stream 401 may include more than about 75% wt., more than about 85% wt. or more than about 95 wt%. non-aromatic hydrocarbons.

[45] The ethylbenzene-enriched product 402 may comprise predominantly ethylbenzene and preferably contains ethylbenzene at a high concentration suitable for direct use in the production of styrene monomer. For example, ethylbenzene-enriched product 402 may contain ethylbenzene in an amount of more than about 90% by weight, more than about 95% by weight, more than about 98% by weight, more than about, 99% wt. or more than about 99.5 wt%. Thus, the ethylbenzene-enriched product 402 obtained in the EB separation module 400, for example, by extractive distillation, is a valuable product that can be obtained during the para-xylene production process described herein. Therefore, this process may alternatively be referred to as a process for the production of para-xylene and ethylbenzene. The ethylbenzene-depleted C ₈ aromatics stream 4B is depleted (or less concentrated) in ethylbenzene than the C ₈ aromatics stream 4 . According to the embodiment shown in FIG. 1, the ethylbenzene-depleted C ₈ aromatics stream 4B from EB separation module 400 is combined with a bypass portion 40 of C ₈ aromatics stream 4 outside of this module to form a combined feed stream 45 of xylene separation zone 200.

[46] In the para-xylene separation zone 200, the para-xylene-rich product 10 is separated as described above, for example, using adsorption separation or crystallization, obtaining a para-xylene depleted effluent stream 6 (for example, a para-xylene depleted raffinate of the adsorption separation process SMB or para-xylene-depleted off-grade filtrate from the crystallization process). In general, the para-xylene depleted effluent stream 6 is depleted (or has a lower concentration) in para-xylene compared to the combined feed stream 45 or otherwise compared to the aromatics stream 4 4. For example, the para-xylene depleted effluent stream 6 may contain para-xylene in an amount of less than about 10% wt., less than about 5% wt. or less, about 2% wt.

[47] The para-xylene depleted effluent 6 is fed into isomerization zone 300 to isomerize the effluent to produce a xylene-equilibrium isomerate 8 in which the concentrations of xylene isomers (ortho-xylene, meta-xylene, and para-xylene) are greater than approach equilibrium relative to the para-xylene-depleted effluent 6. In general, the xylene-equilibrium isomerate 8 is also enriched (or has a higher concentration) in para-xylene compared to the para-xylene-depleted effluent 6. For example, the xylene-equilibrium isomerate 8 may contain para-xylene in an amount of more than about 10% wt., more than about 20% wt. or more, about 30 wt%. All or part of the xylene-equilibrium isomerate 8 can then be recycled to the xylene column 100.

[48] In accordance with the alternative embodiments of the invention shown in FIGS. 2 and 3, it can be appreciated that the EB separation module 400 can be used to remove ethylbenzene from various process streams. Although these figures show the return, or recombination, of the respective ethylbenzene-depleted streams to the same stream, part of which was sent to EB separation (for example, by extractive distillation), in general, ethylbenzene-depleted streams can be returned to any point in the process or, otherwise case used for other purposes. As shown in FIG. 2, a portion 6A of the para-xylene depleted effluent stream 6 is fed to the EB separation module 400 for separation, for example by extractive distillation of the non-aromatic enriched stream 401 and the ethylbenzene enriched product 402 as described above. EB separation module 400 produces an ethylbenzene-depleted and para-xylene effluent stream 6B that is depleted (or less concentrated) in ethylbenzene compared to the para-xylene-depleted effluent stream 6. As shown in FIG. 2, the ethylbenzene-para-xylene depleted effluent 6B from EB separation module 400 is combined with a portion 60 of the para-xylene depleted effluent 6 bypassed outside of this module to form a combined feed stream 65 of isomerization zone 300.

[49] As shown in FIG. 3, a portion 8A of the xylene equilibrium isomerate 8 is fed to the EB separation module 400 for separation, for example by extractive distillation, of the non-aromatic rich stream 401 and the ethylbenzene rich product 402 as described above. In the EB separation module 400, an ethylbenzene-depleted xylene equilibrium isomerate 8B is obtained, which is depleted in (or less concentrated in) ethylbenzene than the xylene-equilibrium isomerate 8. As shown in FIG. 3, ethylbenzene-depleted xylene equilibrium isomerate 8B from EB separation module 400 is combined with a portion 80 of xylene equilibrium isomerate 8 bypassed outside of this module to form a combined stream 85 recycled to xylene column 100.

[50] In some cases, the embodiment of the invention shown in FIG. 3, in which the ethylbenzene-enriched product 402 is separated from the xylene-equilibrium isomerate portion 8A 8, may provide additional benefits. They may be related to the residual amount of extractant used in the EB separation module 400 (for example, the extractive distillation zone) directly into the xylene column 100, and not into the para-xylene separation zone 200 or isomerization zone 300, where this extractant can interfere with the processes. occurring in these zones. Minor losses of the extractant from the extractive distillation zone 400, for example, can lead to its presence in the ethylbenzene-depleted streams 4B, 6B, 8B, as described above, therefore, its immediate removal into the C ₉ ⁺ hydrocarbon stream may be an advantageous solution in this case. separated in the column 100 xylene.

[51] In accordance with each of the embodiments of the invention shown in FIG. 1-3, it is understood that such methods include forming a para-xylene production process loop comprising: (i) a C ₈ aromatics stream 4 (or portion 40 thereof) separated as a low-boiling fraction (or overhead) in a xylene column 100, (ii) a para-xylene depleted effluent stream 6 (or a portion 60 thereof) separated in a xylene separation zone 200 from a C ₈ aromatics stream 4 (or a portion 40 thereof), and (iii) a xylene equilibrium isomerate 8 (or a portion thereof 80) obtained by isomerizing the para-xylene-depleted effluent stream 6 (or part 60 thereof) in isomerization zone 300 . The process can be supplemented by recycling the xylene-equilibrium isomerate 8 (or part 80) to the xylene column 100. Advantageously, the EB separation module 400 can be used to remove the ethylbenzene-enriched product 402 from this loop to simultaneously achieve the benefits of reducing the ethylbenzene concentration in the loop and recovering it as a high value product. According to exemplary embodiments of the invention, each of the following streams: C ₈ aromatics stream 4, para-xylene depleted effluent stream 6, and xylene equilibrium isomerate 8 contains less than about 25 wt. ethylbenzene. As shown in more detail in FIG. 1-3, an untreated ethylbenzene-containing feed stream 2 can continuously flow into this loop, while an ethylbenzene-rich product 402, a para-xylene-rich product 10, and optionally a non-aromatic rich stream 401 can be continuously withdrawn from the loop, with the accumulation of ethylbenzene and, optionally, the non-aromatic compounds in the loop are regulated by the integration of the EB separation module 400. Specific types of non-aromatic compounds that may be present in the non-aromatic stream 401, and therefore may be removed from the para-xylene production loop, include non-aromatic hydrocarbons as described above, namely C ₈ paraffinic hydrocarbons (e.g., n-octane and isomers of iso-octane), C ₇ -C ₈ cycloparaffin hydrocarbons (eg ethylcyclohexane and cyclooctane) and/or C ₉ naphthenic hydrocarbons (eg trimethylcyclohexane isomers).

[52] FIG. 4 shows another embodiment of the invention in which ethylbenzene and optionally non-aromatic compounds are also removed from the process. However, in this embodiment, the ethylbenzene-rich product 402 and optionally the non-aromatics-rich stream 401 are separated by the EB separation module 400, into which all or part of the crude ethylbenzene-containing feed stream 2 is fed. That is, the method according to this embodiment , may include separating the ethylbenzene-enriched product 402 from the entire crude ethylbenzene-containing feed stream 2, or otherwise the portion 2A of that stream, in which case the bypass portion 20 outside the separation module EB is fed to the xylene column 100. In either case, at least a portion of the ethylbenzene-depleted feed stream 2B may be combined with the _C8 aromatics stream 4 separated as a low-boiling fraction (e.g., overhead) in xylene column 100 to form a combined ethylbenzene-depleted aromatics feed stream 43 From ₈ . At least a portion of stream 43 may then be fed to xylene separation zone 200, and then this stream 43, together with C ₈ aromatics stream 4, para-xylene depleted effluent stream 6, and xylene equilibrium isomerate 8, may form a steam production loop. -xylene as described above with respect to the embodiments of the invention shown in FIG. 1-3. However, the embodiment of the invention shown in FIG. 4 is characterized in that ethylbenzene is separated downstream of this circuit. Therefore, although parameters such as total para-xylene yield, total ethylbenzene conversion, and total aromatic ring loss may fall within the ranges given above, these parameters can be determined for the total amount of xylenes, ethylbenzene, and aromatics introduced into the process in the crude containing ethylbenzene. feed stream (eg, in the portion 2A supplied to the EB separation module 400 and the portion 20 bypassed outside of this module) downstream to the para-xylene production process loop. In addition, other parameters associated with this circuit, such as the concentration of ethylbenzene, may be as described above, for example, in relation to the embodiments of the invention shown in FIG. 1-3.

[53] In accordance with the embodiment of the invention shown in FIG. 4, in ^the EB separation module 400, for example, using _{extractive distillation, in addition to the ethylbenzene-enriched product 402, a heavy fraction 47 enriched in C 9 +} ^hydrocarbons can be obtained. .

[54] When controlling the accumulation of ethylbenzene in the process circuit for the production of para-xylene, parts 4A, 6A, 8A, respectively, stream 4 aromatic hydrocarbons C ₈ depleted in para-xylene effluent stream 6 and/or xylene-equilibrium isomerate 8, which are removed from the ethylbenzene separation loop, or otherwise, the 2A portion of the crude ethylbenzene-containing feed stream (the embodiment of the invention shown in FIG. 4) can be changed. As parts 2A, 4A, 6B, 8A increase, the concentration of ethylbenzene in the loop decreases directionally, and the process requirements (e.g., equipment and supplies) associated with the streams forming the loop, namely, para-xylene separation zone 200 and isomerization zone 300, also soften. However, the technological requirements for the EB compartment module 400 are becoming more stringent. Conversely, when portions 2A, 4A, 6B, 8A are reduced, the concentration of ethylbenzene in the loop increases directionally, and the process requirements (e.g., equipment and facilities) associated with the streams forming the loop, namely, the para-xylene separation zone 200 and the zone 300 isomerization, increase. However, the technology requirements for the EB compartment module 400 are relaxed. It will be appreciated by those skilled in the art based on the present disclosure that any particular integrated para-xylene production/extractive distillation process can be implemented with this tradeoff in mind.

[55] To characterize the mutual influence of the size of the portions 4A, 6B, 8A withdrawn from the para-xylene production process loop, or otherwise the portion 2A of the crude ethylbenzene-containing feed stream (the embodiment shown in FIG. 4) and the concentration of ethylbenzene in this loop, the para-xylene depleted effluent stream 6 and the xylene-equilibrium isomerate 8 can serve as convenient references. Both of these streams are below the para-xylene separation zone 200 and generally can have the same or approximately the same flow rate. In accordance with exemplary embodiments of the invention, (i) crude ethylbenzene-containing feed stream 2 or part 2A thereof, (ii) part 4A of C ₈ aromatics stream 4, (iii) part 6A of para-xylene depleted effluent stream 6, or (iv) part 8A of the xylene-equilibrium isomerate 8 that enters the EB separation module 400 (or from which the ethylbenzene-enriched product 402 is separated) can generally range from about 1% wt. up to about 95 wt%. para-xylene-depleted effluent stream 6 or xylene-equilibrium isomerizate 8. However, more typically, such a portion of 2A, 4A, 6A, 8A or all of the crude ethylbenzene-containing feed stream 2 is from about 3% wt. up to about 50% wt., often from about 5% wt. up to about 15% wt. para-xylene depleted effluent stream 6 or xylene-equilibrium isomerate 8, which usually have a comparable flow rate. In accordance with other exemplary embodiments of the invention, (i) crude ethylbenzene containing feed stream 2 or part 2A thereof, (ii) part 4A of C ₈ aromatics stream 4, (iii) part 6A of para-xylene depleted effluent stream 6 or (iv) the portion 8A of the xylene-equilibrium isomerate 8 that enters the EB separation module 400 (or from which the ethylbenzene-enriched product 402 is separated) may generally contain from about 3% by weight. up to about 50% wt. ethylbenzene. However, more typically, such part 2A, 4A, 6A, 8A, or all of the crude ethylbenzene-containing feed stream 2 contains from about 10% wt. up to about 40% wt., often from about 15% wt. up to about 25% wt. ethylbenzene.

[56] In accordance with specific embodiments of the invention, in which a desirable compromise is achieved between the size of the portions 4A, 6B, 8A output from the para-xylene production process loop, or, otherwise, the portion 2A of the raw ethylbenzene-containing feed stream (embodiment shown in Fig. 4) and the concentration of ethylbenzene in this circuit and preferably between (i) the size of the part 2A, 4A, 6B, 8A, determined relative to the para-xylene depleted effluent stream 6 or the xylene-equilibrium isomerate 8 (for example, expressed percentage flow rate of part 2A relative to flow rate of para-xylene-depleted effluent stream 6 or xylene-equilibrium isomerate 8; percentage flow rate of part 4A relative to flow rate of para-xylene-depleted effluent stream 6 or xylene-equilibrium isomerate 8; percentage flow rate of part 6A relative to flow rate depleted in para-xylene effluent stream 6 or xylene-equilibrium isome rizata 8; or percentage flow rate of part 8A relative to the flow rate of the para-xylene depleted effluent stream 6 or xylene equilibrium isomerate 8) and (ii) the concentration of ethylbenzene in the para-xylene depleted effluent stream 6 or xylene equilibrium isomerate 8, the value of (i) may be from about 5% wt. up to about 15% wt., and the value (ii) can be from about 15% wt. up to about 25% wt. For example, the value of (i) can be from about 7% wt. up to about 11% wt., and the value (ii) can be from about 16% wt. up to about 20% wt. Otherwise, when a smaller portion is removed from the para-xylene production loop, or otherwise, a smaller portion of 2A enters the EB separation module 400 (the embodiment shown in Fig. 4), and the concentration of ethylbenzene in this loop is higher, value (i) can be from about 4 wt%. up to about 8% wt., and the value (ii) can be from about 23% wt. up to about 27 wt%.

Conditions in the isomerization zone

[57] When operating a para-xylene production loop integrated with an EB separation module, such as an extractive distillation zone, to prevent excessive accumulation of ethylbenzene in the loop, the benefits are to mitigate the conditions in the isomerization zone 300, which is associated with reduced requirements for conversion of ethylbenzene, and a corresponding reduction in aromatic ring loss, as described above. Therefore, in typical process embodiments, the conversion of ethylbenzene introduced into the para-xylene production loop (eg, under steady state conditions) is less than about 20%. In other exemplary process embodiments, losses of aromatic rings introduced into the para-xylene production loop (eg, under steady state conditions) are less than about 5%.

[58] The isomerization zone may include one or more separate isomerization reactors that have an appropriate isomerization catalyst with different catalyst bed configuration (eg, fixed bed or moving bed) and flow configuration (eg, axial flow or radial flow). Often a single reactor is used. Typical isomerization conditions in the isomerization reactor are from about 150°C (302°F) to about 500°C (932°F), preferably from about 200°C (392°F) to about , 300°C (572°F) and an absolute pressure of from about 1.5 MPa (218 psi) to about 5 MPa (725 psi), preferably from about 2.5 MPa (363 psi) to , approximately 4.5 MPa (653 psi). The isomerization conditions may further include a weight hour space velocity (WHSV) relative to the weight flow rate of the paraxylene-depleted effluent stream and/or any other hydrocarbon-containing stream entering the isomerization reactor (e.g., ethylbenzene- and paraxylene-depleted effluent stream 6B, as described above) from about 0.5 h ^-1 to about 20 h ^-1 , preferably from about 1 h ^-1 to about 10 h ^-1 . As is known in the art, WHSV is the weight flow rate of the reactor feed stream divided by the weight of the catalyst in the reactor and represents the amount of feed stream processed per hour, equivalent to the weight of the catalyst bed. WHSV is inversely proportional to the residence time in the reactor.

[59] Hydrogen can be introduced into the isomerization reactor, typically in a gaseous mixture (eg, containing recycled hydrogen gas) in varying degrees of purity. The hydrogen/hydrocarbon molar ratio relative to the molar flow rate of the paraxylene-depleted effluent stream and/or any other hydrocarbon-containing stream entering the isomerization reactor (e.g., the ethylbenzene- and paraxylene-depleted effluent stream 6B as described above) can generally be from 0.5:1 to about 15:1, typically from about 0.5:1 to about 10:1. Advantageously, however, in view of the milder isomerization conditions possible in the processes described herein, the isomerization reactor of the isomerization zone 300 can be operated in liquid phase mode without the addition of hydrogen. That is, the isomerization zone 300 may include an isomerization reactor through which the para-xylene depleted effluent stream 6, or at least a portion 60 thereof, passes in the liquid phase.

[60] In the reactor in the isomerization zone 300, in general, there is a catalyst whose function may be to perform a given isomerization of ortho-xylene and meta-xylene to para-xylene, but which does not have the function of converting ethylbenzene, for example, by isomerization or dealkylation (cracking ). Thus, the catalyst compositions used in the isomerization reactor can be advantageously simplified by integration with the extractive distillation zone 400 for separating ethylbenzene compared to catalysts meeting conventional ethylbenzene conversion requirements. For example, the acidity of the isomerization catalyst support can be reduced, thereby reducing the degree of dealkylation of ethylbenzene and therefore reducing the amount of light hydrocarbons and other by-products that reduce the yield of the desired para-xylene.

[61] Typical isomerization catalysts used in the isomerization reaction zone contain a metal component and a molecular sieve component, which may be a zeolite or non-zeolite, optionally an inorganic oxide component. Exemplary zeolite aluminosilicate molecular sieves are pentasil type zeolites such as MFI, MEL, MTW, MFS, MTF and FER structure type zeolites, MWW, beta zeolite or mordenite. Typical non-zeolite molecular sieves include molecular sieves with one or more AEL framework types, such as SAPO-11, or with one or more ATO framework types, such as MAPSO-31 (see "Atlas of Zeolite Structure Types", Butterworth- Heineman, Boston, MA, ^3rd ed., 1992). Typical metal components of isomerization catalysts are at least one noble metal and optionally at least one non-noble modifier metal in addition to or instead of at least one noble metal. The noble metals are platinum group metals selected from the group consisting of platinum, palladium, rhodium, ruthenium, osmium, iridium and mixtures thereof. The base metals may be selected from the group consisting of rhenium, tin, germanium, lead, iron, cobalt, nickel, indium, gallium, zinc, uranium, dysprosium, thallium and mixtures thereof. The metal component may also include combinations of one or more base metals and/or one or more noble metals. The total content of the metal(s) in the isomerization catalyst is typically from about 0.01% to about 10% by weight, typically from about 0.01% to about 3% by weight. The total molecular sieve content of the isomerization catalyst is typically from about 1% to about 99% by weight, typically from about 10% to about 90% by weight, often from about 25 % to about 75% by weight. An additional component of the isomerization catalyst may be an inorganic oxide such as a binder (eg alumina). A typical isomerization catalyst for use in the isomerization reactor includes platinum in the amount indicated above, relative to the total metal content of the zeolite aluminosilicate molecular sieve.

Extractive distillation zone

[62] As described herein, extractive distillation or other separation of ethylbenzene is performed in the EB separation module 400 on (i) the crude ethylbenzene-containing feed stream 2 or portion 2A thereof, (ii) the portion 4A of C ₈ aromatics stream 4, ( iii) a portion 6A of the para-xylene depleted effluent stream 6 or (iv) a portion 8A of the xylene equilibrium isomerate 8 fed to this module. For brevity, this stream may generally be referred to as the 2A/4A/6A/8A portion fed to the EB Separation Module (where 2A may refer to the entire crude ethylbenzene containing feed stream 2), all or part of which may be combined with one or several extractants described in this document, with the formation of a liquid mixture. The extractant effectively promotes desired separation of the ethylbenzene-enriched product 402 by increasing the relative volatility of ethylbenzene relative to other C ₈ aromatics (eg, ortho-xylene, meta-xylene, and/or para-xylene). In addition, the extractant itself is easily separated from the distillate (for example, can be recovered as an extractive distillation bottoms) enriched in other(s) aromatic compound(s) C ₈ , as well as the extractant, compared with part 2A/4A/ 6A/8A supplied to the EB separation module, or otherwise a fraction of these respective streams. This makes it possible to advantageously reuse (recycle) the extractant, for example in a continuous extractive distillation process.

[63] A typical extractive distillation process is the distillation of a liquid mixture containing the 2A/4A/6A/8A portion fed to the EB Separation Module (where the 2A portion may be all or part of the crude ethylbenzene containing feed stream 2) and an extractant as described herein. Part 2A/4A/6A/8A or a fraction thereof may be considered a hydrocarbon component containing ethylbenzene and one or more other C ₈ aromatics. Therefore, specific processes include the distillation of a liquid mixture containing ethylbenzene, other C ₈ aromatics (eg, ortho-xylene, meta-xylene and/or para-xylene) and an extractant.

[64] The degree of effectiveness of an extractant can be expressed as its ability to increase the relative volatility of ethylbenzene compared to at least one other C ₈ aromatic compound to be separated (for example, at least one of the xylenes, at least two of xylenes or all xylenes: ortho-xylene, meta-xylene and para-xylene), thereby increasing the separation efficiency at each stage of vapor-liquid equilibrium. In accordance with typical embodiments of the invention, the extractant(s) may be present in the liquid mixture in such an amount that the relative volatility (α) of ethylbenzene compared to at least one other C ₈ aromatic compound is at least about 1, 14, preferably at least about 1.16, more preferably at least about 1.20, even more preferably at least about 1.22 at a given pressure, such as 200 millibars absolute.

[65] Alternatively, the degree of effectiveness of an extractant in the extractive distillation processes described herein can be described in terms of its competitive factor relative to ethylbenzene and other _C8 aromatic compound(s) (e.g., meta-xylene and/or or para-xylene) to be separated from ethylbenzene. The competitive factor (D) can be quantified as follows:

The numerator of this ratio for D is the weight ratio in the vapor phase of ethylbenzene to another C ₈ aromatic at 80°C (176°F) and atmospheric pressure in equilibrium with liquid mixture (i) 1 wt. parts of 60% ethylbenzene and 40% of another aromatic compound WITH ₈ and (ii) 5 wt. parts of an extractant (or a mixture of two or more extractants). The ratio denominator for D is the vapor phase weight ratio of the same compounds at 80°C (176°F) and atmospheric pressure in equilibrium with a liquid mixture consisting of (i) only. Thus, D values greater than one mean an improvement in terms of increased vapor phase separability of ethylbenzene as a result of the presence of the extractant. Therefore, the competitive factor can be measured according to a standard protocol, for example, as described herein. Advantageously, according to typical extractive distillation processes, the competitive factor may be generally at least 1.10, usually at least 1.18, often at least 1.20. In other cases, the extractant may have a competition factor (D) less than one, for example, in general, at most about 0.95, usually, at most about 0.90, often, at most, about 0.85, which means that this extractant helps to increase the separability of a less volatile other C ₈ aromatic compound (for example, meta-xylene or para-xylene) into the liquid phase.

[66] In some embodiments of the invention, alternatively or in combination with the presence of a competitive factor relative to ethylbenzene or other(their) aromatic compound(s) C ₈ as described above, a typical extractant or mixture of extractants may be characterized by a competitive factor with respect to one or more non-aromatic hydrocarbons and ethylbenzene greater than or less than one. Advantageously, the extractant(s) can thereby facilitate the separation of such non-aromatic hydrocarbons from ethylbenzene and other C ₈ aromatic compound(s), for example by enriching the low-boiling fraction or overhead with such non-aromatic hydrocarbons, as described above. in detail below for the case of the non-aromatic hydrocarbon removal column 445 (FIG. 5), downstream to the extractive distillation column 455 (FIG. 5). In accordance with some embodiments of the invention, a typical extractant(s) may be characterized by a competitive factor D, defined as described above, while the weight ratios in the numerator and denominator correspond to the weight ratio of this non-aromatic compound to ethylbenzene, and are greater than one . According to particular embodiments of the invention, the extractant(s) may have a competitive factor D(i) relative to n-octane and ethylbenzene, generally at least about 2.0, typically at least about 2.3, often , at least about 2.6, (ii) relative to ethylcyclohexane and ethylbenzene, generally at least about 1.7, typically at least about 1.9, often at least about 2.1 and/or (iii) relative to cyclooctane and ethylbenzene, generally at least about 1.6, typically at least about 1.7, often at least about 1.8.

[67] In exemplary embodiments, the desired relative volatility (α), competitive factor (D), and/or other operating parameters that favor extractive distillation are obtained by distilling a liquid mixture at subatmospheric pressure, e.g., absolute pressure, generally less than about , 800 millibars, usually less than about 400 millibars, often less than about 300 millibars, while exemplary pressure ranges are from about 50 millibars to about 800 millibars, from about 100 millibars to, about 400 millibars and from about 150 millibars to about 300 millibars.

[68] An exemplary flow diagram corresponding to a typical extractive distillation zone 400 (such as an EB separation module 400) is shown in FIG. 5. According to this embodiment, the portion 2A/4A/6A/8A fed to the extractive distillation zone 400 (where portion 2A may be the entire crude ethylbenzene containing feed stream 2) and containing both ethylbenzene and other(s) aromatic(s) compound(s) C ₈ (for example, ortho-xylene, meta-xylene and/or para-xylene), but also one or more non-aromatic compounds (for example, non-aromatic hydrocarbons, such as isomers of trimethylcyclohexane and/or n -octane) is subjected to prior distillation in the non-aromatic hydrocarbon removal column 445. A non-aromatic extractant stream 410 (selective for the extractive distillation of non-aromatic compounds such as non-aromatic hydrocarbons) may be connected to the 2A/4A/6A/8A portion either before or within the non-aromatic hydrocarbon removal column 445 to facilitate targeted removal of at least one of the non-aromatic compounds (for example, non-aromatic hydrocarbons). As shown in the figure, an optional non-aromatic extractant make-up stream 412A may also be fed, continuously or intermittently, to the non-aromatic hydrocarbon removal column 445 to replace any loss of non-aromatic extractant not recovered in recycle stream 422. The overhead as rich in non-aromatic compound a stream 401 enriched in at least one non-aromatic compound and depleted in at least one C ₈ aromatic compound compared to part 2A/4A/6A/8A is removed from the non-aromatic hydrocarbon removal column 445. This removes at least one non-aromatic compound whose boiling point can be compared to within 15°C (+/-15°C or +/-27°F), up to 10°C (+/-10° C or +/-18°F) or possibly up to 5°C (+/-5°C or +/-9°F) with the boiling point of the aromatic compound(s) C ₈ (for example, ortho- xylene, meta-xylene and/or para-xylene) in part 2A/4A/6A/8A. The non-aromatic hydrocarbon removal column 445 can also be used to remove water from portion 2A/4A/6A/8A, for example, until some water content is reached in the pretreated bottoms 414 and/or liquid mixture (LM). Alternatively, portion 2A/4A/6A/8A may be treated in a separate optional water removal step downstream of the non-aromatic hydrocarbon removal column 445. The removal of water can have economic benefits as it reduces the total amount of material subjected to extractive distillation and hence the associated energy consumption. There may also be other advantages in terms of separation parameters.

[69] The pretreated bottoms 414 is removed from the non-aromatic hydrocarbon removal column 445 (ie, after the previous distillation) as a purified extractive distillation feed stream. This purified feed stream, compared to part 2A/4A/6A/8A, is enriched in ethylbenzene and other C ₈ aromatic compound(s), and optionally also enriched in the non-aromatic compound extractant that was introduced into the removal column 445 non-aromatic hydrocarbon in the non-aromatic extractant stream 410. The pretreated bottoms 414 is also depleted compared to part 2A/4A/6A/8A in one or more non-aromatic compounds present in this stream. The pretreated bottoms 414 is then fed to the extractive distillation column 455 along with the recycle portion 422B of the recycle stream (or second bottoms) 422 containing the ethylbenzene extractant, namely the extractant described herein. The pretreated bottoms 414 and the recycle portion 422B may be connected either before or within the extractive distillation column 455. The recycle portion 422B may provide some or all (at least a portion) of the extractant fed to the extractive distillation column 455. As shown in the figure, an optional extractant make-up stream 412B may also be fed, continuously or intermittently, to the extractive distillation column 455 to replace any loss of extractant not recovered in the recycle stream 422.

[70] The extractive distillation column 455 distills the liquid mixture (LM) containing the pretreated bottoms 414 and the extractant present in the recycle portion 422B and optional make-up stream 412B. Extractive distillation produces an ethylbenzene-enriched product 402 which, compared to the pretreated bottoms 414 and also compared to the liquid mixture (LM), is enriched in ethylbenzene and depleted in extractant and at least one other C ₈ aromatic compound (e.g., one or more xylene isomers) present in the pre-treated bottoms 414. The extractive distillation column 455 also produces a bottoms 418 that, compared to the pre-treated bottoms 414 and also compared to the liquid blend (LM), is at least , one other C ₈ aromatic compound and an extractant, and is depleted in ethylbenzene. To purify and recover the extractant, bottoms 418 are then distilled into an extractant recovery column 465 to produce a second bottoms 422 that is enriched in extractant compared to bottoms 418 and optionally also enriched in non-aromatic compound extractant. Second bottoms 422 is also depleted in at least one other C ₈ aromatic compared to bottoms 418. Thus, at least a portion of second bottoms 422 can be recovered and recycled as recycle portion 422B to extractive distillation column 455 to conserve material resources by providing at least a portion of the liquid mixture (LM) extractant. Optionally, at least a second portion of second bottoms 422 may also be recycled as non-aromatic extractant stream 422C to non-aromatic hydrocarbon removal column 445. In accordance with some embodiments of the invention, second bottoms 422, recycle portion 422B, and/or non-aromatic extractant stream 422C may be further purified (e.g., using additional distillation, adsorbent separation, extraction, etc.) to remove impurities. from these extractant-containing streams before being fed to the respective columns. Optionally, second bottoms bleed stream 422A may be used to prevent excessive accumulation of undesirable impurities in the recycled extractant. In accordance with the embodiment of the invention shown in FIG. 4, all or part of the second bottoms bleed stream 422A (FIG. 5) may correspond to a C ₉ ⁺ enriched heavy fraction 47, which may be combined with the C ₉ ⁺ hydrocarbon stream exiting xylene column 100 as a low-boiling fraction. (for example, the bottom shoulder strap).

[71] Distillation of bottoms 418 in extractant recovery column 465 also produces (i) an ethylbenzene-depleted feed stream 2B, (ii) an ethylbenzene-depleted _C8 aromatics stream 4B, (iii) an ethylbenzene-para-xylene-depleted effluent stream 6B, or ( iv) the ethylbenzene-depleted xylene equilibrium isomerate 8B, which is fed into the para-xylene production loop in case (i) and returned to the para-xylene production loop (e.g., combined with the appropriate bypass portions outside of the extractive distillation as described above) in case (ii), (iii) and (iv). For brevity, this stream may generally be referred to as the 2A/4A/6A/8A depleted ethylbenzene portion fed to or returned to the para-xylene production loop after extractive distillation. Stream 2A/4A/6A/8A, compared to bottoms 418, is rich in at least one other C ₈ aromatic (e.g., ortho-xylene, meta-xylene, and/or para-xylene) and depleted in extractant and optionally also depleted in the extractant of a non-aromatic compound. Thus, as a whole, the extractive distillation zone 400 advantageously produces an ethylbenzene-rich product 402, which is purified to ethylbenzene, a non-aromatic enriched stream 401, which is purified to non-aromatic compounds, and an ethylbenzene-depleted stream 2A/4A/6A/8A, additional an overhead that is enriched in at least one other C ₈ aromatic. Thus, in the extractive distillation zone 400, the successful separation of these purified products is ensured, while also ensuring the recirculation of the extractant. If desired, one or both of these products may be further purified (eg, using further distillation, adsorbent separation, extraction, etc.) to a higher degree of purity.

[72] In accordance with the specific embodiment of the invention shown in FIG. 5, the extractant used in the upstream non-aromatic hydrocarbon removal column 445 as well as in the extractive distillation column 455 (and, in each case, separated from the second bottoms 422) may be the same compound. Alternatively, different extractants can be used for this purpose, in which case an optimal separation (eg, distillation) can be used to produce a non-aromatic extractant stream 422C and a recycle portion 422B, which are fed to the respective columns. An example of a non-aromatic extractant is acetonitrile. Preferably, however, the same compound can be used in both cases of extractive distillation, which provides additional advantages in terms of process simplification (eg, reduced separation requirements) and associated cost savings. As shown in FIG. 5, the total non-aromatic extractant feed 410 to the non-aromatic hydrocarbon removal column 445 may be the sum of the non-aromatic extractant make-up stream 412A and the non-aromatic extractant stream 422C. In addition, the total ethylbenzene extractant feed 416 to the extractive distillation column 455 may be the sum of the make-up stream 412B and the recycle portion 422B.

Extractants

[73] For the extractants used in the described methods, in particular in the extractive distillation zone 400 (such as the EB separation module 400), the binding energy of the extractant and ethylbenzene is predominantly different from the binding energy of the extractant and at least one other ( eg other than ethylbenzene) C ₈ aromatic compound such as ortho-xylene, meta-xylene or para-xylene. The binding energy is determined by a combination of several factors related to the respective interacting compounds, including their polarity and steric effects. Surprisingly, it has been found that extractants with a carbocyclic (e.g. also aromatic) or heterocyclic ring structure substituted in those positions where possible with (i) at least one NR ^a R ^b radical (i.e., the substituent -NR ^a R ^b ), where R ^a and R ^b are independently selected from the group consisting of an oxygen radical, a hydrogen radical, and an alkyl radical containing from about 1 to about 20 carbon atoms, and (ii) at least , two halogen radicals (i.e., halogen substituents formed by the corresponding halogen atoms) are effective extractants for extractive distillation, for example, when used to separate ethylbenzene from at least one other C ₈ aromatic compound (for example, ortho- xylene, meta-xylene and/or para-xylene). Without wishing to be bound by any particular theory, it is believed that the presence of both nitrogen and halogen atoms simultaneously with the cyclic (eg, aromatic) ring structure provides proper polarity, while the cyclic (eg, aromatic) base structure itself provides significant steric effects. As a result, extractants having this combination of characteristics can be mutually attracted to _C8 aromatics other than ethylbenzene, but mutually repel each other with ethylbenzene, thereby facilitating the distillation separation of _C8 aromatics other than ethylbenzene, in particular xylenes, and extractant(s) in the bottom draw, and ethylbenzene in the top draw.

[74] In accordance with typical embodiments of the invention, the extractant is a compound corresponding to formula (I):

,

,

where R ^a and R ^b are each attached to the nitrogen atom shown in this formula and are independently selected from the group consisting of an oxygen radical, a hydrogen radical, and an alkyl radical comprising from about 1 to about 20 carbon atoms. R ^a and R ^b are each connected to the nitrogen atom shown at the top of formula (I) by a single covalent bond, a double covalent bond, or a resonant stabilized covalent bond.

или, в качестве альтернативы, с резонансной стабилизацией как

. В том случае, когда и R^a, и R^b являются водородом, радикальная группа -NR^aR^b представляет собой первичную аминогруппу (-NН₂).When both R ^a and R ^b are an oxygen radical, the radical group -NR ^a R ^b is a nitro group (-NO ₂ ) substituent on the benzene ring of formula (I), where the nitro structure can be represented as

or alternatively with resonant stabilization as

. When both R ^a and R ^b are hydrogen, the radical group -NR ^a R ^b is a primary amino group (-NH ₂ ).

In other cases, R ^a and R ^b together with the nitrogen atom shown in formula (I) above, to which they are usually associated, may form a five- to eight-membered ring, wherein one or more ring members (for example, ring members that are carbon atoms) may be substituted. Suitable substituents on these ring members are those defined below as substituents (1) or (2) on one or more carbon atoms of the alkyl radical. According to exemplary embodiments, NR ^a R ^b may form a five-membered ring substituent such as pyrrolyl, dihydropyrrolyl, tetrahydropyrrolyl, or pyrrolidinyl; or, alternatively, may form a six-membered ring substituent such as pyridinyl, dihydropyridinyl, tetrahydropyridinyl, or piperidinyl.

In the above formula (I), R ² -R ⁶ are substituents on the benzene ring of this formula (other than the substituent NR ^a R ^b ) and are independently selected from the group consisting of halogen, a hydrogen radical, and an alkyl radical including from, about , 1 to about 20 carbon atoms. Preferably, at least one of R ² -R ⁶ is halogen, as is the case when at least one of R ² -R ⁶ is chlorine. For example, R ³ and R ⁴ can both be halogen, such as chlorine. Alternatively, R ² and R ³ may be halogen, such as chlorine.

[75] When one or more of Ra, Rb, R2, R3, R4, ^R5 , or ^R6 is an alkyl radical of from about 1 to about 20 carbon atoms, such alkyl radical refers to a saturated or partially unsaturated, straight chain, branched chain or cyclic hydrocarbon radical in which one or more carbon atoms are optionally substituted and/or replaced, for example substituted according to (1) and/or (2) as defined below , or replaced in accordance with (3) defined below. In particular, in typical hydrocarbon radicals containing from about 1 to about 20 carbon atoms,

[76] (1) one or more carbon atoms attached to one or more hydrogen atoms (i.e., hydrogen radicals), optionally substituted with a monovalent radical independently selected from alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO ₂ H, -SO ₃ H, -NH ₂ , -NO ₂ , -CO ₂ H, -CONH ₂ , -CN, -F, -Cl, -Br and -I, while, in monovalent heteroatomic radicals -OH, -SH, -SOH, -SO ₂ H, -SO ₃ H, -NH ₂ , -CO ₂ H, -CONH ₂ , optionally, one or more bonded hydrogen atoms independently replaced by alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO ₂ H, -SO ₃ H, -NH ₂ , -NO ₂ , -CO ₂ H, - CONH ₂ , -CN, -F, -Cl, -Br or -I;

[77] (2) one or more carbon atoms bonded to two or more hydrogen atoms, optionally substituted with a divalent radical independently selected from ═O, ═S, ═NH, ═NOH, and ═NNH ₂ , wherein, in the divalent heteroatomic radicals =NH, =NOH and =NNH ₂ , optionally, one or more bonded hydrogen atoms (i.e., hydrogen radicals) are independently replaced by alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, - SH, -SOH, -SO ₂ H, -SO ₃ H, -NH ₂ , -NO ₂ , -CO ₂ H, -CONH ₂ , -CN, -F, -Cl, -Br or -I;

[78] (3) one or more carbon atoms of methylene (-CH ₂ -), optionally replaced by a divalent radical independently selected from alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -O-, -S- , -NH-, -OCO-, -CO ₂ -, -CONH-, -OCONH- and -CO ₂ NH-, while, in divalent heteroatomic radicals -NH-, -CONH-, -OCONH- and -CO ₂ NH- one or more hydrogen radicals are independently replaced by alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO ₂ H, -SO ₃ H, -NH ₂ , -NO ₂ , -CO ₂ H, -CONH ₂ , -CN, -F, -Cl, -Br or -I.

[79] In accordance with other embodiments of the invention, one or both of R ^a and R ^b and/or one or more of R ² , R ³ , R ⁴ , R ⁵ or R ⁶ (for example, those substituents R ² , R ³ , R ⁴ , R ⁵ or R ⁶ that are not halogen) may otherwise be independently selected in addition to a hydrogen radical or an alkyl radical of from about 1 to about 20 carbon atoms as defined above, from monovalent heteroatomic radicals such as -OH, -SH, -SOH, -SO ₂ H, -SO ₃ H, -NH ₂ , -NO ₂ , -CO ₂ H, -CONH ₂ and -CN, while, in monovalent heteroatomic radicals -OH, -SH, -SOH, -SO ₂ H, -SO ₃ H, -NH ₂ , -CO ₂ H and -CONH ₂ , optionally, one or more hydrogen radicals are independently replaced by alkyl, alkenyl, alkynyl , cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO ₂ H, -SO ₃ H, -NH ₂ , -NO ₂ , -CO ₂ H, -CONH ₂ , -CN, -F , -Cl, -Br or -I.

[80] An exemplary alkyl radical of from about 1 to about 20 carbon atoms can be a saturated or partially unsaturated hydrocarbon, straight chain, branched chain, or cyclic radical, in which, optionally, none of the carbon atoms is substituted. in accordance with (1), as above, or in which no carbon atom is substituted in accordance with (2), as above, or in which no carbon atom is substituted in accordance with (3), as above . In the case of a saturated cyclic hydrocarbon radical, a typical alkyl radical may be cycloalkyl (eg cyclopentyl or cyclohexyl). In the case of a partially unsaturated cyclic hydrocarbon radical, a typical alkyl radical may be aryl (eg cyclopentadienyl or phenyl).

[81] An exemplary alkyl radical of from about 1 to about 20 carbon atoms can be a saturated, straight chain, branched or cyclic aliphatic hydrocarbon radical in which, optionally, no carbon atom is substituted according to ( 1) as above, or in which no carbon atom is substituted according to (2) as above, or in which no carbon atom is substituted according to (3) as above.

[82] A typical alkyl radical of from about 1 to about 20 carbon atoms may be selected from the group consisting of yl alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, (cycloalkyl) alkyl, (heterocycloalkyl )alkyl, aralkyl, heteroaralkyl, hydroxy, alkoxy, cycloalkoxy, aryloxy, hydroxycarbonyl, hydroxycarbonylalkyl, alkanoyl, alkanoyloxy, alkoxycarbonyl, thiol, alkylthiol, amino, halo, haloalkyl, amido, alkylamido, (cycloalkyl)amido, (heterocycloalkyl)amido, arylamido and (heteroaryl)amido.

[83] A typical alkyl radical of from about 1 to about 20 carbon atoms can be alkyl, such as C ₁ -C ₄ alkyl (eg, methyl, ethyl, propyl, and butyl).

[84] In accordance with other embodiments of the invention, one or both of R ^a and R ^b and/or one or more of R ² , R ³ , R ⁴ , R ⁵ or R ⁶ (for example, those substituents R ² , R ³ , R ⁴ , R ⁵ or R ⁶ that are not halogen), for example both R ^a and R ^b and/or all R ² , R ³ , R ⁴ , R ⁵ or R ⁶ that are not halogen are hydrogen radicals.

[85] In specific embodiments, the aromatic compound of the extractant may be an isomer of dichloronitrobenzene, for example, a compound in which the -NR ^a R ^b group is a nitro group (-NO ₂ ), two of the substituents R ² , R ³ , R ⁴ , R ⁵ or R ⁶ are chlorine and the remaining substituents R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are hydrogen. In the particular case when NR ^a R ^b is a nitro group (-NO ₂ ); R ³ and R ⁴ are chlorine; and R ² , R ⁵ and R ⁶ are hydrogen, the aromatic compound of the extractant is 1,2-dichloro-4-nitrobenzene. In the particular case when NR ^a R ^b is a nitro group (-NO ₂ ); R ² and R ³ are chlorine; and R ⁴ , R ⁵ and R ⁶ are hydrogen, the aromatic compound of the extractant is 1,2-dichloro-3-nitrobenzene. The compounds 1,2-dichloro-4-nitrobenzene and 1,2-dichloro-3-nitrobenzene have the following structure:

[86] In accordance with other specific embodiments of the invention, the aromatic compound of the extractant may be an isomer of dichloroaniline, for example, a compound in which NR ^a R ^b is an amino group (-NH ₂ ), two of the substituents R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are chlorine and the remaining substituents R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are hydrogen. In the particular case when NR ^a R ^b is an amino group (-NH ₂ ); R ³ and R ⁴ are chlorine; and R ² , R ⁵ and R ⁶ are hydrogen, the aromatic compound of the extractant is 3,4-dichloroaniline. This connection has the following structure:

[87] Mixtures of any two or more extractants, such as two or more compounds corresponding to formula (I) above, can also be used, for example, in a liquid mixture (LM) in the extractive distillation process described above. According to specific embodiments, a mixture of dichloroanaline isomer and dichloronitrobenzene isomer may be used, such as a mixture of (i) 3,4-dichloroaniline and (ii) 1,2-dichloro-4-nitrobenzene or 1,2-dichloro-3- nitrobenzene in any ratio (e.g. 5/95 w/w (i):(ii), 25/75 w/w (i):(ii), 50/50 w/w (i) :(ii), 75/25 w/w (i):(ii) or 95/5 w/w (i):(ii)).

[88] In the context of the present invention and in accordance with accepted chemical nomenclature of radicals such as substituent groups,

[89] "Halogen", alone or in combination, means a halogen radical selected from fluorine, chlorine, bromine and iodine (ie, -F, -Cl, -Br and -I, respectively). According to preferred embodiments of the invention, "halogen" means fluorine or chlorine, more preferably chlorine.

[90] "Alkyl", alone or in combination with other radicals (i.e., alone or in combination), means a straight or branched saturated hydrocarbon radical attached at one end of the chain (for example, as in the methyl group, -CH ₃ ) or two ends of the chain (for example, as in the methylene group, -CH ₂ -). Unless otherwise indicated, alkyl includes from 1 to 10 carbon atoms. "Alkenyl", alone or in combination, means alkyl having one or more carbon-carbon double bonds. "Alkynyl", alone or in combination, means alkyl having one or more carbon-carbon triple bonds.

[91] "Cycloalkyl", alone or in combination, means a monocyclic, bridged monocyclic, bicyclic, tricyclic or spirocyclic saturated hydrocarbon radical, which can be connected to the primary molecule at one or more (for example, one or two) bond sites, while , each ring contains 3 to 8 carbon atoms. "Heterocycloalkyl", alone or in combination, means a cycloalkyl in which one or more carbon atoms are replaced by oxygen, nitrogen or sulfur (including sulfoxide and sulfone) or otherwise replaced by a divalent radical including such a heteroatom, for example, = NH, =NOH, =NNH ₂ , =SO and =SO ₂ . "Aryl", alone or in combination, means an unsaturated or partially unsaturated monocyclic, bridged monocyclic, bicyclic, tricyclic or spirocyclic hydrocarbon radical, which can be connected to the primary molecule at one or more (for example, one or two) bond sites, while , each ring contains 3 to 8 carbon atoms. "Heteroaryl", alone or in combination, means aryl in which one or more carbon atoms are replaced by an oxygen, nitrogen or sulfur heteroatom, or otherwise replaced by a divalent radical including such a heteroatom, for example, =NH, =NOH, =NNH ₂ , =SO and =SO ₂ . Unless otherwise indicated or implied by the name of a particular cycloalkyl, heterocycloalkyl, aryl, or heteroaryl radical, these cyclic radicals may be connected to the described molecules at any ring position available for the connection (i.e., at any ring position where substitution is possible ).

[92] "Aralkyl", alone or in combination, means alkyl in which the hydrogen atom is replaced by aryl. "Aralkenyl", alone or in combination, means alkenyl in which a hydrogen atom has been replaced by an aryl. "Aralkynil", alone or in combination, means alkynyl in which a hydrogen atom has been replaced by an aryl. "Heteroaralkyl", "heteroaralkenyl" and "heteroaralkynyl", individually or in combination, mean alkyl, alkenyl and alkynyl, respectively, in which the hydrogen atom is replaced by heteroaryl.

[93] "Hydroxy", alone or in combination, means the -OH radical. "Alkoxy", "alkenoxy" and "alkynyloxy", alone or in combination, means alkyl, alkenyl and alkynyl, respectively, which are connected to the molecule via an -O- bond. For example, alkoxy, alone or in combination, means an alkyl-O- radical. "Cycloalkoxy", "heterocycloalkoxy", "aryloxy" and "heteroaryloxy", alone or in combination, means cycloalkyl, heterocycloalkyl, aryl and heteroaryl, respectively, connected to the molecule via an -O- bond.

[94] "Carbonyl", alone or in combination, means the radical -(C=O)-. "Thiocarbonyl", alone or in combination, means the radical -(C=S)-. "Hydroxycarbonyl", alone or in combination, means the formic acid radical -(C=O)-OH. "Alkanoyl", "alkenoyl", "alkynoyl", individually or in combination, means alkyl, alkenyl and alkynyl, respectively, which are connected to the molecule by a carbonyl bond. For example, alkanoyl, alone or in combination, means an alkyl-(C=O)- radical. "Cycloalkanoyl", "heterocycloalkanoyl", "aroyl" and "heteroaroyl", alone or in combination, means cycloalkyl, heterocycloalkyl, aryl and heteroaryl, respectively, which are connected to the molecule by a carbonyl bond.

[95] "Carbonyloxy", alone or in combination, means a carbonyl that is connected to the molecule via an -O- bond. "Alkanoyloxy", "alkenoyloxy", "alkynoyloxy", "cycloalkanoyloxy", "heterocycloalkanoyloxy", "aroyloxy" and "heteroaroyloxy", alone or in combination, means alkanoyl, alkenoyl, alkinoyl, cycloalkanoyl, heterocycloalkanoyl, aroyl and heteroaroyl, respectively, which are connected to the molecule through an -O- bond. For example, alkanoyloxy means an alkyl-C(=O)-O- radical.

[96] "thiol", alone or in combination, means a -S- or -SH bond. "Alkylthiol", "alkenylthiol" and "alkynylthiol", individually or in combination, mean alkyl, alkenyl and alkynyl, respectively, which are connected to the molecule via an -S- bond. For example, alkylthiol means an alkyl-S- radical. "Thioalkyl", "thiolalkenyl" and "thiolalkynyl", individually or in combination, mean radicals of the formula HS-alkyl-, HS-alkenyl- and HS-alkynyl-, respectively.

[97] The term "amino", alone or in combination, embraces both primary (-NH ₂ ) and secondary (-NH-) amine radicals. Unless otherwise indicated, both primary and secondary amino radicals may be substituted on the hydrogen, or both hydrogens in the case of primary amines, with one or two radicals independently selected from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, aryl, and heteroaryl. "Alkylamino", "alkenylamino" and "alkynylamino", individually or in combination, mean alkyl, alkenyl and alkynyl, respectively, connected to the molecule via a secondary amine bond (-NH-). "Amido", alone or in combination, means the carbonylamine radical -(C=O)-NH-. "Alkylamido", "alkenylamido" and "alkynylamido", alone or in combination, means alkyl, alkenyl and alkynyl, respectively, which are connected to the molecule by an amido bond. For example, "alkylamido" means alkyl-(C=O)-NH-. "Imino", alone or in combination, means the radical -(C=NH)-, while, unless otherwise indicated, imino can be substituted on the hydrogen by the radical defined above in relation to amino.

[98] "Heteroatom(s)", "heteroatomic(s) group(s)" and "heteroatomic(s) radical(s)" means oxygen, nitrogen and sulfur atoms, as well as groups and radicals including these heteroatoms, such as =O, =S, =NH, =NOH and =NNH ₂ .

[99] The following examples are given as representative of the present invention. These examples should not be construed as limiting the scope of the invention, as these and other equivalent embodiments of the invention will become apparent from a consideration of this description and the appended claims.

Example 1

[100] By means of process simulation, the economics of para-xylene production were compared in a conventional aromatics processing plant and in a plant in which an extractive distillation process is integrated, in particular, where distillation with the extractant described above is used to separate ethylbenzene and its removal from the technological circuit. The comparison was based on the separation occurring between the para-xylene separation zone and the xylenes isomerization zone, as shown in FIG. 2. In addition to explaining the operation of the upstream reformate separator, simulations of the xylene column distillation, para-xylene separation and isomerization steps described above are performed. For better applicability of the simulation results to industrial processes, the operation of the C ₇ (toluene)/C ₉ transalkylation (disproportionation) module was also included in the simulation. The separation of para-xylene in each case was based on crystallization.

[101] Three separate cases were identified and analyzed. In the first case, defined as "conventional", extractive distillation was not used, its simulation was based on the use of a conventional isomerization catalyst active in relation to the dealkylation of ethylbenzene to limit the accumulation of ethylbenzene in the process loop. The second case, defined as "EB-X 18%", was modeled on the basis of the depleted para-xylene effluent from the para-xylene separation zone, then fed to the extractive distillation column, containing 18% wt. ethylbenzene. The third case, defined as "EB-X 25%" was modeled on the basis of the same threads containing 25% wt. ethylbenzene. Due to the higher concentration of ethylbenzene in the process circuit, in the third case, only 6 wt% was required for extractive distillation. depleted in para-xylene effluent stream compared to 9% wt. in the second case. Thus, the simulation showed the expected trade-off between the concentration of recycled ethylbenzene and the portion of the recycled stream fed to extractive distillation. In both cases, EB-X 18% and EB-X 25%, the requirement for the conversion of ethylbenzene on the isomerization catalyst was removed, therefore, milder operating conditions were used in the simulation of the isomerization reactor, including operation in the liquid phase without the addition of hydrogen.

[102] Based on the study of the simulation results, the expected costs in the "normal", "EB-X 18%" and "EB-X 25%" cases were comparable. Although the latter two cases required additional capital costs associated with extractive distillation implementation, it was found that this could be offset by cost savings due to reduced load on other process steps, of which the 50% reduction in isomerization costs is the most significant.

[103] In terms of overall operating costs (including facilities) for simulated cases based on the use of an extractive distillation step, significant savings are achieved in hydrogen consumption, which is estimated to be only about 40% compared to the "normal" case due to the lack of supply hydrogen into the isomerization zone. In addition, in terms of product yield and the corresponding value of the product streams, simulations of the isomerization reaction occurring in the liquid phase in the second and third cases showed a much lower estimated aromatic ring loss compared to the "normal" case. Other simulation benefits for 18% EB-X and 25% EB-X operating with an extractive distillation step included >2% increase in total aromatics unit liquid product and >15% reduction in off-gas generation. In addition, about 6.5% wt. the total liquid product in the cases EB-X 18% and EB-X 25% was recovered as high purity ethylbenzene suitable for the production of styrene monomer. In the "normal" case, corresponding to existing commercial para-xylene production plants, there was no such stream of opportunity to generate income.

[104] For the cases of simulated plants producing approximately 309,000 kg/h (2.6 million metric tons per year) of para-styrene, the technological effect (additional product cost minus additional operating costs) from the introduction of extractive distillation of ethylbenzene in cases of EB- X 18% and EB-X 25% were estimated at $70-80 million per annum compared to the "normal" case, assuming a crude oil price of approximately $50/bbl.

[105] In general, aspects of the invention relate to processes for the production of para-xylene using distillation steps to separate a C ₈ aromatics stream, then separate the para-xylene-enriched product from that stream, and isomerize the remaining para-xylene-depleted effluent stream to produce additional amount of para-xylene. By providing a recycle loop to the distillation step and/or downstream separation of the para-xylene-enriched product, said additional amount can also be recovered. Advantageously, the use of extractive distillation or other separation to remove ethylbenzene and optionally other low boiling compounds (eg non-aromatic C ₉ hydrocarbons) improves the economics of the process to the extent that conventional ethylbenzene conversion requirements in the isomerization zone can be relaxed and can to obtain a product - purified ethylbenzene.

[106] Specialists in this field based on the information obtained from the present description, it will be clear that in the described methods, various changes are possible without going beyond the scope of the invention. The mechanisms used to explain theoretical or observed phenomena or results should be interpreted as illustrative only and not as in any way limiting the scope of the appended claims.

Claims (36)

1. A method for the production of para-xylene, including the steps in which: separating in a xylene column a C ₈ aromatic hydrocarbon stream and a C ₉ ⁺ hydrocarbon stream from at least a portion of the ethylbenzene-containing feed stream; separating the xylene-rich product from at least a portion of the C ₈ aromatics stream in a xylene separation zone to form a para-xylene-depleted effluent stream; in the isomerization zone, isomerization of at least a portion of the para-xylene-depleted effluent stream is carried out to obtain a xylene-equilibrium isomerizate; recycle at least a portion of the xylene equilibrium isomerate to the xylene column and the ethylbenzene separation module (EB) separates the ethylbenzene-rich product from (i) a portion of the ethylbenzene-containing feed stream to form an ethylbenzene-depleted feed stream, and combines at least a portion of the ethylbenzene-depleted feed stream with all or part of the _C8 aromatics stream (ii ) a portion of the C ₈ aromatics stream to form an ethylbenzene-depleted C ₈ aromatics stream, and connect at least a portion of the ethylbenzene-depleted C ₈ aromatics stream to a portion of the C ₈ aromatics stream conducted through a bypass outside the EB separation module (iii) part of the paraxylene depleted effluent stream to form an ethylbenzene and paraxylene depleted effluent stream, and connect at least a portion of the ethylbenzene and paraxylene depleted effluent stream to a portion of the paraxylene depleted effluent flowing through a bypass outside the EB separation module (iv) parts of xylene-equal oat isomerate to form an ethylbenzene-depleted xylene-equilibrium isomerate and combine at least a portion of the ethylbenzene-depleted xylene-equilibrium isomerate with a portion of the xylene-equilibrium isomerate conducted bypass outside the EB separation module, or (v) a combination thereof, moreover, the EB separation module contains extractive distillation, and extractants are used with a carbocyclic (for example, also aromatic) or heterocyclic ring structure substituted at ring positions where substitution (i) with at least one NR radical is possible^aR^b (i.e. substituent -NR^aR^b), and R^a and R^b independently selected from the group consisting of an oxygen radical, a hydrogen radical, and a hydrocarbyl radical of from about 1 to about 20 carbon atoms, and (ii) at least two halogen radicals (i.e., halogen substituents formed from their respective halogen atoms). 2. The process of claim 1 wherein the ethylbenzene-rich product is separated from a portion of the paraxylene-depleted effluent stream to produce an ethylbenzene-paraxylene-depleted effluent stream. 3. The process of claim 1, wherein the crude ethylbenzene-containing feed stream contains a naphtha reformer, naphtha cracker, or transalkylation product. 4. The method of claim 3 wherein the naphtha cracking product is pyrolysis gasoline. 5. The process of claim 1, wherein the xylene separation zone includes adsorption separation or crystallization to separate the para-xylene-enriched product. 6. The process of claim 1 wherein the isomerization zone includes an isomerization reactor through which at least a portion of the para-xylene depleted effluent stream is passed in the liquid phase. 7. The process of claim 7, wherein the isomerization reactor is operated under isomerization conditions comprising a temperature of from about 200°C (392°F) to about 300°C (572°F) and an absolute pressure of from about 2.5 MPa (363 psi) to approximately 4.5 MPa (653 psi). 8. The process of claim 1, wherein the para-xylene production loop is closed by recycling said at least a portion of the xylene equilibrium isomerizate to the xylene column. 9. The process of claim 1, wherein (i) or a portion of an ethylbenzene-containing feed stream, (ii) a portion of a C ₈ aromatics stream, (iii) a portion of a para-xylene depleted effluent stream, or (iv) a portion of a xylene equilibrium isomerate , from which the product enriched with ethylbenzene is separated, is from about 1% wt. up to about 95 wt%. para-xylene depleted effluent stream or xylene-equilibrium isomerizate. 10. The process of claim 1, wherein (i) a feed stream containing ethylbenzene or a portion thereof, (ii) a portion of a C ₈ aromatics stream, (iii) a portion of a para-xylene depleted effluent stream, or (iv) a portion of a xylene equilibrium isomerate , from which the product enriched with ethylbenzene is separated, contains from about 3% wt. up to about 50% wt. ethylbenzene. 11. A process for the production of para-xylene, in which a process loop for the production of para-xylene is formed, containing: (i) a C ₈ aromatic hydrocarbon stream separated as a low-boiling fraction in a xylene column, (ii) a para-xylene depleted effluent stream separated in a zone separating xylene from at least a portion of the C ₈ aromatics stream, and (iii) a xylene equilibrium isomerate obtained by isomerizing at least a portion of the para-xylene depleted effluent stream, wherein the process loop is closed by recycling at least a portion of the xylene-equilibrium isomerizate to the xylene column, and while the total conversion of ethylbenzene introduced into the process circuit for the production of para-xylene is less than about 20 wt%. or at the same time, the total loss of aromatic rings introduced into the process circuit for the production of para-xylene is less than about 5% mol., wherein the method further comprises removing an ethylbenzene-enriched product containing ethylenebenzene in an amount of more than 90% by weight. from a para-xylene depleted effluent from a para-xylene production loop or from a xylene-equilibrium isomerate from a para-xylene production loop, moreover, the removal of the product enriched in ethylbenzene is carried out by extractive distillation, and extractants with a carbocyclic (for example, also aromatic) or heterocyclic ring structure substituted at ring positions where substitution (i) with at least one NR radical is possible^aR^b (i.e. substituent -NR^aR^b), and R^a and R^b independently selected from the group consisting of an oxygen radical, a hydrogen radical, and a hydrocarbyl radical of from about 1 to about 20 carbon atoms, and (ii) at least two halogen radicals (i.e., halogen substituents formed from their respective halogen atoms). 12. The method according to p. 11, in which more than 80 wt%. ethylbenzene introduced into the para-xylene production process loop is present in the ethylbenzene-containing feed stream entering the xylene column and/or the ethylbenzene separation module (EB). 13. The process of claim 11, wherein isomerization of at least a portion of the para-xylene-depleted effluent is carried out with a one-time aromatic ring loss of less than about 2%. 14. The method according to p. 11, in which each of (i), (ii) and (iii) process circuit contains less than about 25 wt%. ethylbenzene. 15. The method according to p. 11, in which enriched with ethylbenzene product contains more than about 95 wt%. ethylbenzene. 16. The method according to p. 15, in which enriched with ethylbenzene product contains more than about 99.5 wt%. ethylbenzene. 17. A method for the production of para-xylene, wherein the method includes the steps in which: separating the ethylbenzene-rich product from a portion of the ethylbenzene-containing feed stream to obtain an ethylbenzene-depleted feed stream; in a xylene column, separating a C ₈ aromatic hydrocarbon stream as a low boiling fraction and a C ₉ ⁺ hydrocarbon stream as a high boiling fraction from a portion of the ethylbenzene-containing feed stream; combining at least a portion of the ethylbenzene-depleted feed stream with the C ₈ aromatics stream to form a combined ethylbenzene-depleted C ₈ aromatics feed stream/stream; in a xylene separation zone, separating the para-xylene-rich product from at least a portion of the combined ethylbenzene-depleted feed stream/C ₈ aromatics stream to obtain a para-xylene-depleted effluent stream; in the isomerization zone, isomerization of at least a portion of the para-xylene-depleted effluent stream is carried out to obtain a xylene-equilibrium isomerizate; And recycle at least part of the xylene-equilibrium isomerizate to the xylene column, moreover, a single conversion of ethylbenzene in the isomerization zone is less than about 5% by weight, and the separation of the product enriched in ethylbenzene is carried out by extractive distillation, using extractants with a carbocyclic (for example, also aromatic) or heterocyclic ring structure substituted at ring positions where substitution (i) with at least one NR radical is possible^aR^b (i.e. substituent -NR^aR^b), and R^a and R^b independently selected from the group consisting of an oxygen radical, a hydrogen radical, and a hydrocarbyl radical of from about 1 to about 20 carbon atoms, and (ii) at least two halogen radicals (i.e., halogen substituents formed from their respective halogen atoms). 18. The method of claim 17, wherein the extractive distillation further produces a C ₉ ⁺ hydrocarbon-rich heavy fraction, and the method further comprises combining the C ₉ ⁺ hydrocarbon-rich heavy fraction with the C ₉ ⁺ hydrocarbon stream separated in the xylene column.

Images